Implants for spinal fixation or fusion

ABSTRACT

The present invention generally relates to bone implants. More specifically, the present invention relates to bone implants used for the fixation or fusion of the sacroiliac joint and/or the spine. For example, a system for fusing or stabilizing a plurality of bones is provided. The system includes an implant structure having stem portion and a head portion, the stem portion having a rectilinear cross sectional area. A tulip or saddle structure can be attached to the head portion, and a rod can be secured within the tulip or saddle structure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/903,410, filed Feb. 23, 2018, and titled “IMPLANTS FOR SPINALFIXATION OR FUSION”, which is a divisional of Ser. No. 14/216,863, filedMar. 17, 2014, now U.S. Pat. No. 9,936,983, and titled “IMPLANTS FORSPINAL FIXATION OR FUSION”, which claims priority to U.S. PatentProvisional Application No. 61/793,803, filed Mar. 15, 2013, and titled“IMPLANTS FOR SPINAL FIXATION OR FUSION”, each of which is hereinincorporated by reference in its entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference. For example,this application incorporates by reference in their entireties U.S.Patent Publication No. 2011/0087294, U.S. Patent Publication No.2011/0087296, U.S. Patent Publication No. 2011/0118785, and U.S. PatentPublication No. 2011/0125268.

FIELD

The present invention generally relates to bone implants. Morespecifically, the present invention relates to bone implants used forthe stabilization, fixation and/or fusion of the sacroiliac joint and/orthe spine.

BACKGROUND

Many types of hardware are available both for the fixation of bones thatare fractured and for the fixation of bones that are to be fused(arthrodesed).

For example, the human hip girdle is made up of three large bones joinedby three relatively immobile joints. One of the bones is called thesacrum and it lies at the bottom of the lumbar spine, where it connectswith the L5 vertebra. The other two bones are commonly called “hipbones” and are technically referred to as the right ilium and—the leftilium. The sacrum connects with both hip bones at the sacroiliac joint(in shorthand, the SI-Joint).

The SI-Joint functions in the transmission of forces from the spine tothe lower extremities, and vice-versa. The SI-Joint has been describedas a pain generator for up to 22% of lower back pain.

To relieve pain generated from the SI-Joint, sacroiliac joint fusion istypically indicated as surgical treatment, e.g., for degenerativesacroiliitis, inflammatory sacroiliitis, iatrogenic instability of thesacroiliac joint, osteitis condensans ilii, or traumatic fracturedislocation of the pelvis. Currently, screws and screws with plates areused for sacroiliac fusion. At the same time the cartilage has to beremoved from the “synovial joint” portion of the SI-Joint. This requiresa large incision to approach the damaged, subluxed, dislocated,fractured, or degenerative joint.

An alternative implant that is not based on the screw design can also beused to fuse the SI-Joint and/or the spine. Such an implant can have atriangular cross-section, for example, as further described below. Toinsert the implant, a cavity can be formed into the bone, and theimplant can then be inserted into the cavity using a tool such as animpactor. The implants can then be stabilized together, if desired, byconnecting the implants with a crossbar or other connecting device.

Therefore, it would be desirable to provide systems, devices and methodsfor SI-Joint and/or spinal stabilization, fixation and/or fusion.

SUMMARY OF THE DISCLOSURE

The present invention generally relates to bone implants. Morespecifically, the present invention relates to bone implants used forthe stabilization, fixation or fusion of the sacroiliac joint and/or thespine.

In some embodiments, a system for fusing or stabilizing a plurality ofbones is provided. The system includes an implant structure having stemportion and a head portion, the stem portion having a rectilinear crosssectional area. A tulip or saddle structure can be attached to the headportion, and a rod can be secured within the tulip or saddle structure.

In general, in one embodiment, a system for fusing or stabilizing aplurality of bones includes an implant structure having stem portion anda head portion, a tulip or saddle structure attached to the headportion, and a rod secured within the tulip or saddle structure. Thestem portion has a rectilinear cross sectional area.

This and other embodiments can include one or more of the followingfeatures. The head portion can be connected to the stem portion with aMorse taper. The head portion can be connected to the stem portion witha screw attachment. The head portion can be integral with the stemportion. The tulip or saddle structure can include a first slot and acavity for receiving the head portion. The tulip or saddle structure canbe rotatable through a 60 degree range of motion.

In general, in one embodiment, an implant for spinal fixation or fusionincludes an elongate body having a stem portion, a head portion, and alongitudinal axis. The stem portion has a rectilinear cross sectionalarea transverse to the longitudinal axis, and a tulip or saddlestructure is attached to the head portion.

This and other embodiments can include one or more of the followingfeatures. The head portion can be connected to the stem portion with aMorse taper. The head portion can be connected to the stem portion witha screw attachment. The screw attachment can be formed on a shank thatextends through the entire length of the elongate body. The head portioncan be integral with the stem portion. The tulip or saddle structure caninclude a first slot and a cavity for receiving the head portion. Thetulip or saddle structure can be rotatable through a 60 degree range ofmotion. The head portion can be connected to the stem portion through anexpandable attachment on the head portion that is secured within acavity in the stem portion. The tulip or saddle structure can beattached to the head portion through a snap on connection which caninclude a slot a receptacle in the tulip or saddle structure forreceiving the head portion.

In general, in one embodiment, a method for stabilizing a first bonesegment and a second bone segment of a patient includes implanting afirst implant into the first bone segment. The first implant includes astem portion configured to be inserted into the first bone segment and atulip portion for receiving a rod. Implanting a second implant into thesecond bone segment includes a stem portion configured to be insertedinto the second bone segment and a tulip portion for receiving the rod.The stem portion of the second implant has a rectilinear cross sectiontransverse to a longitudinal axis of the stem portion of the secondimplant. The method further includes securing a rod to both the tulipportion of the first implant and the tulip portion of the secondimplant.

This and other embodiments can include one of more of the followingfeatures. The first implant can be a pedicle screw. The first implantcan have a stem portion having a rectilinear cross section transverse toa longitudinal axis of the first implant. The first bone segment can bea vertebrae and the second bone segment can be the sacrum.

In general, in one embodiment, a method for pedicle screw salvageincludes: (1) removing a pedicle screw from a bone segment to leave acavity in the bone segment; and (2) inserting an implant into thecavity. The implant has a stem portion configured to be inserted intothe bone segment and a tulip portion for receiving a rod. The stemportion has a rectilinear cross sectional profile transverse to alongitudinal axis of the stem portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe claims that follow. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates an embodiment of an implant structure.

FIGS. 2A-2D are side section views of the formation of a broached borein bone according to one embodiment of the invention.

FIGS. 2E and 2F illustrate the assembly of a soft tissue protectorsystem for placement over a guide wire.

FIGS. 3 and 4 are, respectively, anterior and posterior anatomic viewsof the human hip girdle comprising the sacrum and the hip bones (theright ilium, and the left ilium), the sacrum being connected with bothhip bones at the sacroiliac joint (in shorthand, the SI-Joint).

FIGS. 5 to 7A and 7B are anatomic views showing, respectively, apre-implanted perspective, implanted perspective, implanted anteriorview, and implanted cranio-caudal section view, the implantation ofthree implant structures for the fixation of the SI-Joint using alateral approach through the ilium, the SI-Joint, and into the sacrum.

FIGS. 8A to 8C illustrate embodiments of an implant structure with ahead portion joined using a Morse taper.

FIG. 9 illustrates an embodiment of an implant structure with a headportion joined using a screw type attachment.

FIGS. 10A and 10B illustrate an embodiment of an implant structure withan integrated head portion.

FIGS. 11A and 11B illustrate embodiments of an implant structuresuitable for pedicle screw salvage.

FIG. 12 illustrates an embodiment of an implant structure with ananchor.

FIGS. 13A and 13B illustrate the attachment of a tulip structure to animplant structure and the securing of a rod to the tulip structure.

FIGS. 14 and 15 illustrate alternative embodiments of head portions withexpandable attachment features.

FIG. 16 illustrates an embodiment of an implant structure with ascrew-like head portion that extends completely through the stem portionof the implant structure.

FIG. 17 illustrates an embodiment of the attachment of the head portionto the stem portion of the implant structure using a ball and socketjoint.

FIGS. 18A to 18E illustrate the head portion of the implant structure inconnection with a tulip structure.

FIGS. 19A and 19B illustrate a lateral view and an axial view of anembodiment of the implant structure crossing the SI-Joint using aposterolateral approach entering from the posterior iliac spine of theilium, angling through the SI-Joint, and terminating in the sacral alae.

FIG. 20A is an anatomic posterior perspective view, exploded prior toimplantation, of a representative configuration of an assembly of one ormore implant structures, sized and configured to achieve translaminarlumbar fusion in a non-invasive manner and without removal of theintervertebral disc.

FIG. 20B is an anatomic inferior transverse plane view showing theassembly shown in FIG. 20A after implantation.

FIG. 21A is an anatomic posterior perspective view, exploded prior toimplantation, of a representative configuration of an assembly of one ormore implant structures, sized and configured to achieve lumbar facetfusion, in a non-invasive manner.

FIG. 21B is an anatomic inferior transverse plane view showing theassembly shown in FIG. 21A after implantation.

FIG. 21C is an anatomic lateral view showing the assembly shown in FIG.21A after implantation.

FIG. 22A is an anatomic posterior view showing, in an exploded viewprior to implantation, another representative configuration of anassembly of one or more implant structures sized and configured toachieve fusion between lumbar vertebra L5 and sacral vertebra S 1, in anon-invasive manner and without removal of the intervertebral disc,using a posterolateral approach entering from the posterior iliac spineof the ilium, angling through the SI-Joint, and terminating in thelumbar vertebra L5.

FIG. 22B is an anatomic posterior view showing the assembly shown inFIG. 22A after implantation.

FIG. 23A is an anatomic anterior perspective view showing, in anexploded view prior to implantation, a representative configuration ofan assembly of one or more implant structures, sized and configured tostabilize a spondylolisthesis at the L5/S1 articulation.

FIG. 23B is an anatomic anterior perspective view showing the assemblyshown in FIG. 23A after implantation.

FIG. 23C is an anatomic lateral view showing the assembly shown in FIG.23B.

FIG. 24 is an axial view illustrating an implant inserted through aposteromedial approach.

DETAILED DESCRIPTION

Elongated, stem-like implant structures 20 like that shown in FIG. 1make possible the fixation of the SI-Joint (shown in anterior andposterior views, respectively, in FIGS. 3 and 4) in a minimally invasivemanner. These implant structures 20 can be effectively implanted throughthe use a lateral surgical approach. The procedure is desirably aided byconventional lateral, inlet, and outlet visualization techniques, e.g.,using X-ray image intensifiers such as a C-arms or fluoroscopes toproduce a live image feed, which is displayed on a TV screen.

In one embodiment of a lateral approach (see FIGS. 5, 6, and 7A/B), oneor more implant structures 20 are introduced laterally through theilium, the SI-Joint, and into the sacrum. This path and resultingplacement of the implant structures 20 are best shown in FIGS. 6 and7A/B. In the illustrated embodiment, three implant structures 20 areplaced in this manner. Also in the illustrated embodiment, the implantstructures 20 are rectilinear in cross section and triangular in thiscase, but it should be appreciated that implant structures 20 of otherrectilinear cross sections can be used.

Before undertaking a lateral implantation procedure, the physicianidentifies the SI-Joint segments that are to be fixated or fused(arthrodesed) using, e.g., the Fortin finger test, thigh thrust, FABER,Gaenslen's, compression, distraction, and diagnostic SI-Joint injection.

Aided by lateral, inlet, and outlet C-arm views, and with the patientlying in a prone position, the physician aligns the greater sciaticnotches and then the alae (using lateral visualization) to provide atrue lateral position. A 3 cm incision is made starting aligned with theposterior cortex of the sacral canal, followed by blunt tissueseparation to the ilium. From the lateral view, the guide pin 38 (withsleeve (not shown)) (e.g., a Steinmann Pin) is started resting on theilium at a position inferior to the sacrum end plate and just anteriorto the sacral canal. In the outlet view, the guide pin 38 should beparallel to the sacrum end plate and in the inlet view the guide pin 38should be at a shallow angle anterior (e.g., 15.degree. to 20.degree.off the floor, as FIG. 7B shows). In a lateral view, the guide pin 38should be posterior to the sacrum anterior wall. In the outlet view, theguide pin 38 should be superior to the first sacral foramen and lateralof mid-line. This corresponds generally to the sequence showndiagrammatically in FIGS. 2A and 2B. A soft tissue protector (not shown)is desirably slipped over the guide pin 38 and firmly against the iliumbefore removing the guide pin sleeve (not shown).

Over the guide pin 38 (and through the soft tissue protector), the pilotbore 42 is drilled in the manner previously described, as isdiagrammatically shown in FIG. 2C. The pilot bore 42 extends through theilium, through the SI-Joint, and into the S1. The drill bit 40 isremoved.

The shaped broach 44 is tapped into the pilot bore 42 over the guide pin38 (and through the soft tissue protector) to create a broached bore 48with the desired profile for the implant structure 20, which, in theillustrated embodiment, is triangular. This generally corresponds to thesequence shown diagrammatically in FIG. 2D. The triangular profile ofthe broached bore 48 is also shown in FIG. 5.

FIGS. 2E and 2F illustrate an embodiment of the assembly of a softtissue protector or dilator or delivery sleeve 200 with a drill sleeve202, a guide pin sleeve 204 and a handle 206. In some embodiments, thedrill sleeve 202 and guide pin sleeve 204 can be inserted within thesoft tissue protector 200 to form a soft tissue protector assembly 210that can slide over the guide pin 208 until bony contact is achieved.The soft tissue protector 200 can be any one of the soft tissueprotectors or dilators or delivery sleeves disclosed herein. In someembodiments, an expandable dilator or delivery sleeve 200 as disclosedherein can be used in place of a conventional soft tissue dilator. Inthe case of the expandable dilator, in some embodiments, the expandabledilator can be slid over the guide pin and then expanded before thedrill sleeve 202 and/or guide pin sleeve 204 are inserted within theexpandable dilator. In other embodiments, insertion of the drill sleeve202 and/or guide pin sleeve 204 within the expandable dilator can beused to expand the expandable dilator.

In some embodiments, a dilator can be used to open a channel though thetissue prior to sliding the soft tissue protector assembly 210 over theguide pin. The dilator(s) can be placed over the guide pin, using forexample a plurality of sequentially larger dilators or using anexpandable dilator. After the channel has been formed through thetissue, the dilator(s) can be removed and the soft tissue protectorassembly can be slid over the guide pin. In some embodiments, theexpandable dilator can serve as a soft tissue protector after beingexpanded. For example, after expansion the drill sleeve and guide pinsleeve can be inserted into the expandable dilator.

As shown in FIGS. 5 and 6, a triangular implant structure 20 can be nowtapped through the soft tissue protector over the guide pin 38 throughthe ilium, across the SI-Joint, and into the sacrum, until the proximalend of the implant structure 20 is flush against the lateral wall of theilium (see also FIGS. 7A and 7B). The guide pin 38 and soft tissueprotector are withdrawn, leaving the implant structure 20 residing inthe broached passageway, flush with the lateral wall of the ilium (seeFIGS. 7A and 7B). In the illustrated embodiment, two additional implantstructures 20 are implanted in this manner, as FIG. 6 best shows. Inother embodiments, the proximal ends of the implant structures 20 areleft proud of the lateral wall of the ilium, such that they extend 1, 2,3 or 4 mm outside of the ilium. This ensures that the implants 20 engagethe hard cortical portion of the ilium rather than just the softercancellous portion, through which they might migrate if there was nostructural support from hard cortical bone. The hard cortical bone canalso bear the loads or forces typically exerted on the bone by theimplant 20.

The implant structures 20 are sized according to the local anatomy. Forthe SI-Joint, representative implant structures 20 can range in size,depending upon the local anatomy, from about 35 mm to about 60 mm inlength, and about a 7 mm inscribed diameter (i.e. a triangle having aheight of about 10.5 mm and a base of about 12 mm). The morphology ofthe local structures can be generally understood by medicalprofessionals using textbooks of human skeletal anatomy along with theirknowledge of the site and its disease or injury. The physician is alsoable to ascertain the dimensions of the implant structure 20 based uponprior analysis of the morphology of the targeted bone using, forexample, plain film x-ray, fluoroscopic x-ray, or MRI or CT scanning.

Using a lateral approach, one or more implant structures 20 can beindividually inserted in a minimally invasive fashion across theSI-Joint, as has been described. Conventional tissue access tools,obturators, cannulas, and/or drills can be used for this purpose.Alternatively, the novel tissue access tools described above and inco-pending U.S. Application No. 61/609,043, titled “TISSUE DILATOR ANDPROTECTER” and filed Mar. 9, 2012, which is hereby incorporated byreference in its entirety, can also be used. No joint preparation,removal of cartilage, or scraping are required before formation of theinsertion path or insertion of the implant structures 20, so a minimallyinvasive insertion path sized approximately at or about the maximumouter diameter of the implant structures 20 can be formed.

The implant structures 20 can obviate the need for autologous bone graftmaterial, additional pedicle screws and/or rods, hollow modularanchorage screws, cannulated compression screws, threaded cages withinthe joint, or fracture fixation screws. Still, in the physician'sdiscretion, bone graft material and other fixation instrumentation canbe used in combination with the implant structures 20.

In a representative procedure, one to six, or perhaps up to eight,implant structures 20 can be used, depending on the size of the patientand the size of the implant structures 20. After installation, thepatient would be advised to prevent or reduce loading of the SI-Jointwhile fusion occurs. This could be about a six to twelve week period ormore, depending on the health of the patient and his or her adherence topost-op protocol.

The implant structures 20 make possible surgical techniques that areless invasive than traditional open surgery with no extensive softtissue stripping. The lateral approach to the SI-Joint provides astraightforward surgical approach that complements the minimallyinvasive surgical techniques. The profile and design of the implantstructures 20 minimize or reduce rotation and micromotion. Rigid implantstructures 20 made from titanium provide immediate post-op SI-Jointstability. A bony in-growth region 24 comprising a porous plasma spraycoating with irregular surface supports stable bone fixation/fusion. Theimplant structures 20 and surgical approaches make possible theplacement of larger fusion surface areas designed to maximizepost-surgical weight bearing capacity and provide a biomechanicallyrigorous implant designed specifically to stabilize the heavily loadedSI-Joint.

To improve the stability and weight bearing capacity of the implant, theimplant can be inserted across three or more cortical walls. Forexample, after insertion the implant can traverse two cortical walls ofthe ilium and at least one cortical wall of the sacrum. The corticalbone is much denser and stronger than cancellous bone and can betterwithstand the large stresses found in the SI-Joint. By crossing three ormore cortical walls, the implant can spread the load across more loadbearing structures, thereby reducing the amount of load borne by eachstructure. In addition, movement of the implant within the bone afterimplantation is reduced by providing structural support in threelocations around the implant versus two locations.

In some embodiments, the implant structure can function like a pediclescrew to allow fixation and/or fusion of bone such as the spine and/orSI-Joint. For example, long constructs can be used to join, fuse and/orstabilize a plurality of vertebrae in the thoracic, lumbar, and sacralportions of the spine. For example, to treat spinal disorders such asdegenerative scoliosis, the L5 vertebra to the S1 vertebrae can be fusedusing a system of implants and rods as described herein. As illustratedin FIGS. 8A-18E, the implant structure can include a stem portion and ahead portion. The stem portion can be formed similarly to the SI-Jointimplants described herein and in co-pending patent application U.S.Provisional No. 61/642,681, filed May 4, 2012, titled “FenestratedImplant” and U.S. Pat. No. 8,202,305 titled “Systems and Method for theFixation or Fusion of Bone.” A tulip or saddle structure can be attachedto the head portion, and a rod can be inserted into and fixed to aplurality of tulip structures attached to implanted implant structures,thereby fusing and/or stabilizing the spine and/or other bones. In someembodiments, the stem portion, head portion, and tulip or saddlestructure can all be cannulated and have a lumen that extendslongitudinally through the assembled structure such that the assembledstructure can be disposed over a guidewire or guide pin.

In some embodiments, as illustrated in FIGS. 8A-8C, the head portion 804can be separate from the stem portion 802. For example, FIGS. 8A-8Cillustrate embodiments of the implant structure 800 with a machine tapersuch as a Morse Taper. In some embodiments as illustrated in FIG. 8A,the head portion 804 can have a ball portion 806 and a tapered shank808. The tapered shank 808 can fit into a corresponding tapering cavity810 in the stem portion 802 to form a taper lock that is held togetherby friction. The length of the tapered shank 808 can be varied, makingthe distance between the ball portion 806 and proximal end of the stemportion 802 variable.

In some embodiments as illustrated in FIG. 8B, the head portion 804 canhave a tapering cavity 810 while the stem portion 802 can have a taperedshank 808 extending from the proximal end of the stem portion 802. Thelength of the tapered shank 808 can be varied so that the distancebetween the head portion 804 and stem portion 802 can be adjusted asdesired. In some embodiments, the tapered shank 808 of the stem portion802 can be angled or curved with respect to the longitudinal axis of thestem portion 802. A curved tapered shank 808 can be useful as describedbelow for the embodiment shown in FIG. 8C.

In some embodiments as illustrated in FIG. 8C, the head portion 804 canhave a ball portion 806 and a tapered shank 808 that is curved or angledsuch that the distal portion of the tapered shank 808 is offset orangled with respect to the ball portion 806 and proximal portion of thetapered shank 808. A curved tapered shank 808 can be useful when asuitable implantation location in one or more bones is not aligned withthe other implantation locations. In order for the implant structures800 to line up with the stabilizing rod, a curved tapered shank 808 canbe used so that the head portions 806 all line up with the stabilizingrod even if the implantation locations do not line up.

FIG. 9 illustrates another embodiment of an implant structure 900 with astem portion 902 and a head portion 904. The head portion 904 can have aball portion 906 and a shank 908. The shank 908 can have threads 910,like a screw, that can be screwed into a cavity 912 with complementaryinternal threads. The ball portion 904 can have a screw drive 914 thatfacilitates turning of the head portion 904. The screw drive 914 can bea slot, socket (square, hex, star, etc.), or other typical screw drive914 mechanism.

FIGS. 10A and 10B illustrate embodiments of integrated implantstructures 1000 having a stem portion 1002 and a head portion 1004 thatis integral with the stem portion 1002. As shown in FIGS. 10A and 10B,the head portion 1004 is integral or fixed to the stem portion 1002, andtherefore the head portion 1004 has a fixed length relative to the stemportion 1002. As shown in FIG. 10A, the head portion 1004 can have aball portion 1006 that can be attached to a tulip portion that isdescribed in further detail below in, for example, FIGS. 13A and18A-18C. Alternatively, as shown in FIG. 10B, the head portion 1004 canhave a tulip portion 1007 integrated directly with the stem portion1002. Having an integrated implant structure 1000 can be useful when itis known in advance that an implant structure 1000 will be used in, forexample, a fixation or stabilization procedure that requires the use ofan implant structure with a head portion 1004. The integrated implant1000 can reduce procedure time by not requiring the attachment of thehead portion 1004 onto the stem portion 1002. In addition, because thehead portion 1004 is integral with the stem portion 1002, the integratedimplant 1000 may have a greater structural integrity or strength than animplant assembled from separate pieces.

In some embodiments that may be particularly suited for pedicle screwsalvage as illustrated in FIGS. 11A and 11B, the implant structure 1100can have a stem portion 1102 with ledges or fenestrations 1003 thatpromote bone ingrowth. Examples of fenestrations that can beincorporated into the implant structure 1100 are described in co-pendingpatent application U.S. Provisional No. 61/642,681, filed May 4, 2012,titled “Fenestrated Implant.” In some embodiments, the outer surfaceand/or structure of the stem portion 1102 can be twisted. In someembodiments, the stem portion 1102 may have a round cross-section tobetter match the cavity within the bone after the old pedicle screw hasbeen removed. In some embodiments, the stem portion 1102 can be tapered.The diameter, shape and profile of the stem portion 1102 can match thebone cavity. In some embodiments, the stem portion 1102 can be oval,round, square, triangular, or rectilinear. In some embodiments, the headportion 1104 can be attached to the stem portion 1102 as describedabove. For example, the head portion 1104 can be attached to the stemportion 1102 using a Morse taper or screw attachment, or the headportion 1104 can be integral with the stem portion. Pedicle screwsalvage can be performed when an implant, such as a pedicle screw,becomes loose within the bone due to windshield wipering or butterflyingeffects caused by stresses exerted to the bone by the implant. The looseimplant can be removed and then replaced by one of the implantsdescribed herein.

FIG. 12 illustrates an implant structure 1200 with a stem portion 1202,a head portion 1204 attached to the proximal end of the stem portion1202, and an anchor 1210 located distally the distal end of the stemportion 1202. The anchor 1210 can be folded into a collapsedconfiguration during insertion of the implant structure 1200 into bone,and then unfolded and/or expanded into an expanded configuration afterinsertion. In some embodiments, the anchor 1210 can have one or more armportions 1212 that are foldable and/or expandable. In some embodiments,the anchor 1210 can be mechanically actuated from the collapsedconfiguration to the expanded configuration. In some embodiments, thearm portions 1212 can be joined at a hinge or a hub 1214. In someembodiments, the arm portions 12 can be expanded like the frame of anumbrella. In other embodiments, the anchor 1210 can be self-expandingand can be made of a shape memory material such as a nickel titaniumalloy. In some embodiments, the anchor 1210 can be restrained by asheath or other restraining element when in the collapsed configuration.In some embodiments, the anchor 1210 can be attached to and/or extendfrom the distal end of the stem portion 1202. The anchor 1210 can reduceor prevent implant structure 1200 migration after implantation.

FIGS. 13A and 13B illustrate an implant structure 1300 and acorresponding tulip or saddle structure 1350 that can be attached to thehead portion 1304 of the implant structure 1300. The tulip structure1350 can have a slot 1352 for receiving a rod 1380 that can be used tostabilize the spine. In some embodiments, the tulip structure 1350 canhave internal threading 1354 on the two wall portions 1356 that form theslot 1352. In some embodiments, a locking screw 1390 can be used to lockand secure the rod 1380 in place within the tulip structure 1350. Thelocking screw 1390 can have threading 1392 that correspond to theinternal threading 1354 on the two wall portions 1356. To lock andsecure the rod in place, the locking screw can simply be screwed inplace over the rod 1380. The locking screw 1390 can have a screw drivesimilar to screw drive 914 described above with respect to FIG. 9. Inother embodiments, other fastening mechanisms can be used in place ofthe locking screw 1390 to hold the rod in place. In some embodiments,the top portions of the wall portions 1356 can be snapped off along abreak line 1358. In some embodiments, the break line 1358 can be formedby scoring or thinning the wall portions 1356 along the break line 1358.In some embodiments, the tulip structure 1350 does not have any breaklines 1358 or excess wall portions 1356 that can be broken off and caninstead have wall portions 1356 that are sized to receive the rod 1380and locking screw 1390 without having excess material extending past thelocking screw 1390.

FIG. 14 illustrates another embodiment of an implant structure 1400having a stem portion 1402 with a cavity 1412 for receiving anexpandable attachment 1410 on the shank 1408 of the head portion 1404.The expandable attachment 1410 on the shank 1408 can have a collapsedconfiguration and an expanded configuration. The entrance to the cavity1412 can be a narrowed opening 1414 with a diameter less than thediameter of the cavity 1412. The shank 1408 can be inserted through thenarrowed opening 1414 and into the cavity 1412 with the expandableattachment 1410 in the collapsed configuration. Once in the cavity 1412,the expandable attachment 1410 can expand into the expandedconfiguration, thereby securing the head portion 1404 to the stemportion 1402. The head portion 1404 can have a ball portion 1406 forconnected to a tulip structure.

FIG. 15 illustrates another embodiment of a head portion 1504 that canbe secured into a cavity 1412 in a stem portion 1402 similar to thatillustrated in FIG. 14. The head portion 1504 can have a ball portion1506 and a shank 1508 with narrowed or undercut portion 1508 and atapered distal portion 1510. The tapered distal portion 1510 has an endthat is narrow enough to be inserted into the narrowed opening 1414. Asthe tapered distal portion 1510 is further inserted through the narrowedopening 1414, the tapered distal portion 1510 forces the narrowedopening to open wider until the narrowed opening snaps into the undercutportion 1508 of the shank 1508, which in combination with the tapereddistal portion 1510 in the cavity, functions to secure the head portion1504 to the stem portion 1402.

FIG. 16 illustrates another embodiment of a head portion 1604 than canbe screwed into an implant structure 1600 in a similar manner asdescribed in connection with FIG. 9, except that in this embodiment, theshank 1608 can have a length that allows the shank 1608 to extendcompletely through the implant structure 1600. Similarly to theembodiment described in FIG. 9, the shank 1608 can be threaded 1610 anda screw drive on the head portion 1604 can be used to turn the screwlike shank 1608. In some embodiments, the threads 1610 on the proximalportion of the shank 1608 can be machine threads for engaging thecorresponding threads in the implant structure 1600. The threads 1610 onthe distal portion of the shank 1608 can be deeper than the machinethreads, which allow the threads to better engage cancellous bone. Insome embodiments, the pitch of the threads 1610 can be constant alongthe length of the shank 1608. In other embodiments, the pitch of thethreads 1610 can vary between the different thread types.

FIG. 17 illustrates another embodiment of the attachment of the stemportion 1702 of an implant structure 1700 to a head portion 1704. Inthis embodiment, the stem portion 1702 has a socket 1708 for receiving acorresponding ball 1706 on the distal end of the head portion 1704. Theball 1706 can reside in the socket 1708 to form a ball and socket jointthat permits the head portion 1704 to be rotated through a predeterminedangle of rotation. In some embodiments, the angle of rotation can beabout 60 degrees or less. In other embodiments, the angle of rotationcan be between about 30 to 90 degrees or less.

FIGS. 18A-18E illustrate embodiments of a snap-on tulip or saddlestructure 1850. In some embodiments, the tulip structure 1850 can have aslot 1852 for receiving a rod that can be used to stabilize the spine orother bones. In some embodiments, the tulip structure 1850 can haveinternal threading on the two wall portions 1856 that form the slot1852. In some embodiments, the wall portions 1856 can have extended tabsthat can be snapped off and removed. In some embodiments, the tulipstructure 1850 can have a head portion receiving slot 1858 shaped toreceive the head portion 1804 attached to the implant structure 1800.The head portion receiving slot 1858 can be located on the distal end ofthe tulip structure 1850 and provides access to the internal cavity ofthe tulip structure 1850. The distal end of the tulip structure can havean opening 1860 that allows a portion of the implant structure 1800 toextend through. The diameter or size of the opening 1860 is less thanthe diameter or size of the head portion 1804, which allows the tulipstructure 1850 to receive and then retain the head portion within thecavity of the tulip structure 1850. A stabilizing rod can then be fixedin place within the slot 1852 of the tulip structure 1850, therebysecuring the head portion 1804 to the tulip structure 1850.

In some embodiments, the head portion receiving slot 1858 runs up both aportion of one of the side walls and the along the bottom portion to theopening 1860. In some embodiments, the upper portion of the head portionreceiving slot 1858 can be circular in shape to accommodate the ballportion of the head portion 1804. The circular portion of the headportion receiving slot 1858 can be located a sufficient distance fromthe bottom portion of the tulip structure 1850 such that after the ballportion of the head portion 1804 passes into the cavity of the tulipstructure 1850, the ball portion drops down against the bottom portionwhich prevents the ball portion from inadvertently sliding out of thetulip structure 1850. In order for the ball portion of the head portion1804 to be removed from the tulip structure 1850, the ball portion mustbe raised from the bottom of the tulip structure 1850 until the ballportion is aligned with the circular portion of the head portionreceiving slot 1858, and then the head portion 1804 can be removed fromthe tulip structure. In some embodiments, the portion of the headportion receiving slot 1858 on the bottom part of the tulip structurecan be a straight slot. In other embodiments, the portion of the headportion receiving slot 1858 on the bottom part of the tulip structurecan be a curved slot.

The shape and structure of the tulip structure 1850 cavity and opening1860 allows the tulip structure 1850 to have about a 60 degree angle ofmovement and rotation after being attached to the head portion 1804.Such a tulip structure 1850 and head portion 1804 can be referred to aspolyaxial, meaning the tulip structure 1850 can freely move within aconical area. In other embodiments, the angle of movement and rotationcan be between about 30 to 90 degrees or less. Having a substantialangle of movement and rotation allows the implant structure 1800 to beinserted in a wider variety of angles while still allowing the tulipstructure 1850 to be aligned with the rod for fixation.

Any of the implants described herein can be used in a variety ofsurgical procedures, such as stabilization, fixation or fusion of thesacroiliac joint and/or the spine, including vertebra and facet joints.In addition, surgical procedures using a posterior or a posterolateralapproach will be particularly suitable for use with the implantstructures described herein since the tulip structure of the implantwill be aligned with the other implants along the spine afterimplantation. As described herein, these implant structures can beconnected together using a rod that can be secured to each tulipstructure. For simplicity, the following procedures will be illustratedand described using a general implant structure 20, but it is understoodthat any of the implant structures described herein can be used in placeof the general implant structure 20.

For example, FIGS. 19A and 19B illustrate a lateral view and an axialview of an embodiment of the implant structure crossing the SI-Jointusing a posterolateral approach entering from the posterior iliac spineof the ilium, angling through the SI-Joint, and terminating in thesacral alae.

The posterolateral approach involves less soft tissue disruption thatthe lateral approach, because there is less soft tissue overlying theentry point of the posterior iliac spine of the ilium. Introduction ofthe implant structure 20 from this region therefore makes possible asmaller, more mobile incision. Further, the implant structure 20 passesthrough more bone along the posterolateral route than in a strictlylateral route, thereby involving more surface area of the SI-Joint andresulting in more fusion and better fixation of the SI-Joint. Employingthe posterolateral approach also makes it possible to bypass all nerveroots, including the L5 nerve root.

The set-up for a posterolateral approach is generally the same as for alateral approach. It desirably involves the identification of theSI-Joint segments that are to be fixated or fused (arthrodesed) using,e.g., the Faber Test, or CT-guided injection, or X-ray/MRI of SI-Joint.It is desirable performed with the patient lying in a prone position (ontheir stomach) and is aided by lateral and anterior-posterior (A-P)c-arms. The same surgical tools are used to form the pilot bore 42 overa guide pin 38, except the path of the pilot bore 42 now starts from theposterior iliac spine of the ilium, angles through the SI-Joint, andterminates in the sacral alae. The pilot bore 42 is shaped into thedesired profile using a broach, as before described, and the implantstructure 20 is inserted into the broached bore 48. The implantstructure 20 is tapped through the soft tissue protector over the guidepin 38 from the posterior iliac spine of the ilium, angling through theSI-Joint, and terminating in the sacral alae, until the proximal end ofthe implant structure 20 is flush against the posterior iliac spine ofthe ilium. Because of the anatomic morphology of the bone along theposterolateral route, it may be advisable to introduce implantstructures of difference sizes, with the most superior being the longestin length, and the others being smaller in length.

FIG. 20A shows, in an exploded view prior to implantation, arepresentative configuration of an assembly of one or more implantstructures 20 sized and configured to achieve translaminar lumbar fusionin a non-invasive manner and without removal of the intervertebral disc.FIG. 20B shows the assembly after implantation, respectively, in aninferior transverse plane view.

As can be seen in the representative embodiment illustrated in FIGS. 20Aand 20B, the assembly comprises two implant structures 20. The firstimplant structure 20 extends from the left superior articular process ofvertebra L5, through the adjoining facet capsule into the left inferiorarticular process of vertebra L4, and, from there, further through thelamina of vertebra L4 into an interior right posterolateral region ofvertebra L4 adjacent the spinous process. The second implant structure20 extends from the right superior articular process of vertebra L5,through the adjoining facet capsule into the right inferior articularprocess of vertebra L4, and, from there, further through the lamina ofvertebra L4 into an interior left posterolateral region of vertebra L4adjacent the spinous process. The first and second implant structures 20cross each other within the medial lamina of vertebra L4.

The first and second implant structures 20 are sized and configuredaccording to the local anatomy. The selection of a translaminar lumbarfusion (posterior approach) is indicated when the facet joints arealigned with the sagittal plane. Removal of the intervertebral disc isnot required, unless the condition of the disc warrants its removal.

A posterior procedure for implanting the assembly of implant structures20 shown in FIGS. 20A and 20B comprises (i) identifying the vertebrae ofthe lumbar spine region that are to be fused; (ii) opening an incision,which comprises, e.g., with the patient lying in a prone position (ontheir stomach), making a 3 mm posterior incision; and (iii) using aguide pin to establish a desired implantation path through bone for thefirst (e.g., left side) implant structure 20, which, in FIGS. 20A and20B, traverses through the left superior articular process of vertebraL5, through the adjoining facet capsule into the left inferior articularprocess of vertebra L4, and then through the lamina of vertebra L4 intoan interior right posterolateral region of vertebra L4 adjacent thespinous process. The method further includes (iv) guided by the guidepin, increasing the cross section of the path; (v) guided by the guidepin, shaping the cross section of the path to correspond with the crosssection of the implant structure; (vi) inserting the implant structure20 through the path over the guide pin; (vii) withdrawing the guide pin;and (viii) using a guide pin to established a desired implantation paththrough bone for the second (e.g., right side) implant structure 20,which, in FIGS. 20A and 20B, traverses through the right superiorarticular process of vertebra L5, through the adjoining facet capsuleinto the right inferior articular process of vertebra L4, and throughthe lamina of vertebra L4 into an interior left posterolateral region ofvertebra L4 adjacent the spinous process. The physician repeats theremainder of the above-described procedure sequentially for the rightimplant structure 20 as for the left, and, after withdrawing the guidepin, closes the incision.

The intimate contact created between the bony in-growth orthrough-growth region 24 along the surface of the implant structure 20across the facet joint accelerates bony in-growth or through-growthonto, into, or through the implant structure 20, to accelerate fusion ofthe facets joints between L4 and L5. Of course, translaminar lumbarfusion between L5 and S1 can be achieved using first and second implantstructures in the same manner.

FIG. 21A shows, in an exploded view prior to implantation, arepresentative configuration of an assembly of one or more implantstructures 20 sized and configured to lumbar facet fusion, in anon-invasive manner and without removal of the intervertebral disc.FIGS. 21B and 21C show the assembly after implantation, respectively, inan inferior transverse plane view and a lateral view.

As can be seen in the representative embodiment illustrated in FIGS. 21Ato 21C, the assembly comprises two implant structures 20. The firstimplant structure 20 extends from the left inferior articular process ofvertebra L4, through the adjoining facet capsule into the left superiorarticular process of vertebra L5 and into the pedicle of vertebra L5.The second implant structure 20 extends from the right inferiorarticular process of vertebra L5, through the adjoining facet capsuleinto the right superior articular process of vertebra L5 and into thepedicle of vertebra L5. In this arrangement, the first and secondimplant structures 20 extend in parallel directions on the left andright pedicles of vertebra L5. The first and second implant structures20 are sized and configured according to the local anatomy. Theselection of lumbar facet fusion (posterior approach) is indicated whenthe facet joints are coronally angled. Removal of the intervertebraldisc is not necessary, unless the condition of the disc warrants itsremoval.

A posterior procedure for implanting the assembly of implant structures20 shown in FIGS. 21A to 21C comprises (i) identifying the vertebrae ofthe lumbar spine region that are to be fused; (ii) opening an incision,which comprises, e.g., with the patient lying in a prone position (ontheir stomach), making a 3 mm posterior incision; and (iii) using aguide pin to established a desired implantation path through bone forthe first (e.g., left side) implant structure 20, which, in FIGS. 21A to21C, traverses through the left inferior articular process of vertebraL4, through the adjoining facet capsule into the left superior articularprocess of vertebra L5 and into the pedicle of vertebra L5. The methodfurther includes (iv) guided by the guide pin, increasing the crosssection of the path; (v) guided by the guide pin, shaping the crosssection of the path to correspond with the cross section of the implantstructure 20; (vi) inserting the implant structure 20 through the pathover the guide pin; (vii) withdrawing the guide pin; and (viii) using aguide pin to establish a desired implantation path through bone for thesecond (e.g., right side) implant structure 20, which, in FIGS. 21A to21C, traverses through the right inferior articular process of vertebraL4, through the adjoining facet capsule into the right superiorarticular process of vertebra L5 and into the pedicle of vertebra L5.The physician repeats the remainder of the above-described proceduresequentially for the right implant structure 20 as for the left and,withdrawing the guide pin, closes the incision.

The intimate contact created between the bony in-growth orthrough-growth region 24 along the surface of the implant structure 20across the facet joint accelerates bony in-growth or through-growthonto, into, or through the implant structure 20, to accelerate fusion ofthe facets joints between L4 and L5.

Of course, transfacet lumbar fusion between L5 and S1 can be achievedusing first and second implant structures in the same manner.

FIG. 22A shows, in an exploded view prior to implantation, anotherrepresentative configuration of an assembly of one or more implantstructures 20 sized and configured to achieve fusion between lumbarvertebra L5 and sacral vertebra S1, in a non-invasive manner and withoutremoval of the intervertebral disc. FIGS. 22B and 22C show the assemblyafter implantation.

As FIGS. 22A and 22B show, the one or more implant structures areintroduced in a posterolateral approach entering from the posterioriliac spine of the ilium, angling through the SI-Joint into and throughthe sacral vertebra S1, and terminating in the lumbar vertebra L5. Thispath and resulting placement of the implant structures 20 are also shownin FIG. 22C. In the illustrated embodiment, two implant structures 20are placed in this manner, but there can be more or fewer implantstructures 20. Also in the illustrated embodiment, the implantstructures 20 are triangular in cross section, but it should beappreciated that implant structures 20 of other cross sections aspreviously described can be used.

The posterolateral approach involves less soft tissue disruption thanthe lateral approach, because there is less soft tissue overlying theentry point of the posterior iliac spine of the ilium. Introduction ofthe implant structure 20 from this region therefore makes possible asmaller, more mobile incision.

The set-up for a posterolateral approach is generally the same as for alateral approach. It desirably involves the identification of the lumbarregion that is to be fixated or fused (arthrodesed) using, e.g., theFaber Test, or CT-guided injection, or X-ray/MRI of the L5-S1 level. Itis desirable performed with the patient lying in a prone position (ontheir stomach) and is aided by lateral and anterior-posterior (A-P)c-arms. The same surgical tools are used to form the pilot bore over aguide pin (e.g., on the right side), except the path of the pilot borenow starts from the posterior iliac spine of the ilium, angles throughthe SI-Joint, and terminates in the lumbar vertebra L5. The broachedbore is formed, and the right implant 20 structure is inserted. Theguide pin is withdrawn, and the procedure is repeated for the leftimplant structure 20, or vice versa. The incision site(s) are closed.

The assembly as described makes possible the achievement of trans-iliaclumbar fusion using a posterolateral approach in a non-invasive manner,with minimal incision, and without necessarily removing theintervertebral disc between L5 and S1.

FIG. 23A shows, in an exploded view prior to implantation, arepresentative configuration of an assembly of one or more implantstructures 20 sized and configured to stabilize the spondylolisthesis atthe L5/S1 articulation. FIGS. 23B and 23C show the assembly afterimplantation.

As shown, the implant structure 20 extends from a posterolateral regionof the sacral vertebra S1, across the intervertebral disc into anopposite anterolateral region of the lumbar vertebra L5. The implantstructure 20 extends in an angled path (e.g., about 20 degrees to about40 degrees off horizontal) through the sacral vertebra S1 in a superiordirection, through the adjoining intervertebral disc, and terminates inthe lumbar vertebra L5.

A physician can employ a posterior approach for implanting the implantstructure 20 shown in FIGS. 23A, 23B, and 23C, which includes forming apilot bore over a guide pin inserted in the angled path from theposterior of the sacral vertebra S1 through the intervertebral disc andinto an opposite anterolateral region of the lumbar vertebra L5, forminga broached bore, inserting the implant structure 20, and withdrawing theguide pin. The incision site is then closed. As previously described,more than one implant structure 20 can be placed in the same manner tostabilize a spondylolisthesis.

The physician can, if desired, combine stabilization of thespondylolisthesis, as shown in FIG. 23A/B/C, with a reduction,realigning L5 and S-1. The physician can also, if desired, combinestabilization of the spondylolisthesis, as shown in FIG. 23A/B/C (withor without reduction of the spondylolisthesis), with a lumbar facetfusion, as shown in FIGS. 21A to 21C. The physician can also, ifdesired, combine stabilization of the spondylolisthesis, as shown inFIG. 23A/B/C, with a decompression, e.g., by the posterior removal ofthe spinous process and laminae bilaterally.

In addition, in some embodiments as shown in FIG. 24, a posteromedialapproach can be used to insert the implant 2400. For example, theimplant 2400 can be inserted through the posterolateral sacrum, acrossthe alae, through the SI-Joint, and into the ilium where the implant mayterminate. As illustrated, the implant 2400 can have a stem portion 2402that is inserted into the bone and a tulip portion 2404 that remainsoutside the bone.

Variations and modifications of the devices and methods disclosed hereinwill be readily apparent to persons skilled in the art. As such, itshould be understood that the foregoing detailed description and theaccompanying illustrations, are made for purposes of clarity andunderstanding, and are not intended to limit the scope of the invention,which is defined by the claims appended hereto. Any feature described inany one embodiment described herein can be combined with any otherfeature of any of the other embodiment whether preferred or not.

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of the appended claims. All publications, patents, and patentapplications cited herein are hereby incorporated by reference for allpurposes.

What is claimed is:
 1. A method for stabilizing a first bone segment anda second bone segment of a patient, the method comprising: implanting afirst implant into the first bone segment, the first implant comprisinga stem portion configured to be inserted into the first bone segment anda tulip portion for receiving a rod; implanting a second implant intothe second bone segment, the second implant comprising a stem portionconfigured to be inserted into the second bone segment and a tulipportion for receiving the rod, the stem portion of the second implanthaving a rectilinear cross section transverse to a longitudinal axis ofthe stem portion of the second implant wherein the stem portion of thesecond implant is straight; and securing a rod to both the tulip portionof the first implant and the tulip portion of the second implant.
 2. Themethod of claim 1, wherein the first implant is a pedicle screw.
 3. Themethod of claim 1, wherein the first implant has a stem portion having arectilinear cross section transverse to a longitudinal axis of the firstimplant.
 4. The method of claim 1, wherein the first bone segment is avertebra and the second bone segment is the sacrum.
 5. A method forstabilizing a vertebra and a sacrum of a patient, the method comprising:implanting a first implant into the vertebra, the first implantcomprising a stem portion configured to be inserted into the vertebraand a tulip portion for receiving a rod; implanting a second implantthrough the sacrum, across the sacroiliac joint and into the ilium, thesecond implant comprising a stem portion configured to extend from thesacrum to the ilium and a tulip portion for receiving the rod, the stemportion of the second implant having a rectilinear cross sectiontransverse to a longitudinal axis of the stem portion of the secondimplant; and securing a rod to both the tulip portion of the firstimplant and the tulip portion of the second implant.
 6. The method ofclaim 5, wherein the first implant is a pedicle screw.
 7. The method ofclaim 5, wherein the first implant has a stem portion having arectilinear cross section transverse to a longitudinal axis of the firstimplant.
 8. The method of claim 5, wherein the stem portion of thesecond implant is straight.
 9. A system for fusing or stabilizing aplurality of bones, the system comprising: an implant structure having astem portion and a head portion, the head portion including a shank thathas a length such that it extends through the stem portion and distallyfrom the stem portion, the implant structure having a linearlongitudinal axis extending along the stem portion and the head portion,the shank having a distal region with external threads that are shapedto interface with corresponding internal threads on the stem portion,the stem portion having a length and a configuration such that it can bestably implanted into and through a sacrum, across a sacroiliac joint,and into an ilium; a tulip or saddle structure attached to the headportion, a proximal end of the head portion spaced from a distal end ofthe shank portion at a distance such that the tulip is secured to theproximal end of the head portion when the distal end of the shank isimplanted in the ilium; and a rod secured within the tulip or saddlestructure.
 10. The system of claim 9, wherein the head portion isconnected to the stem portion with a Morse taper.
 11. The system ofclaim 9, wherein the head portion is connected to the stem portion witha screw attachment.
 12. The system of claim 9, wherein the head portionis integral with the stem portion.
 13. The system of claim 9, whereinthe tulip or saddle structure comprises a first slot and a cavity forreceiving the head portion.
 14. The system of claim 9, wherein the tulipor saddle structure is rotatable through a 60 degree range of motion.15. An implant for spinal fixation or fusion, the implant comprising: anelongate body having a stem portion, a head portion, and a linearlongitudinal axis, the head portion including a shank with a length suchthat it extends through the stem portion and distally from the stemportion, the shank having a distal region with external threads that areshaped to interface with corresponding internal threads on the stemportion, the stem portion having a length and a configuration such thatit can be stably implanted into and through a sacrum, across asacroiliac joint, and into an ilium; and a tulip or saddle structureattached to the head portion, a proximal end of the head portion spacedfrom a distal end of the shank portion at a distance such that the tulipis secured to the head portion when the distal end of the shank isimplanted in the ilium.
 16. The implant of claim 15, wherein the headportion is connected to the stem portion with a Morse taper.
 17. Theimplant of claim 15, wherein the head portion is connected to the stemportion with a screw attachment.
 18. The implant of claim 17, whereinthe screw attachment is formed on a shank that extends through theentire length of the stem portion.
 19. The implant of claim 15, whereinthe head portion is integral with the stem portion.
 20. The implant ofclaim 15, wherein the tulip or saddle structure comprises a first slotand a cavity for receiving the head portion.
 21. The implant of claim15, wherein the tulip or saddle structure is rotatable through a 60degree range of motion.
 22. The implant of claim 15, wherein the headportion is connected to the stem portion through an expandableattachment on the head portion that is secured within a cavity in thestem portion.
 23. The implant of claim 15, wherein the tulip or saddlestructure is attached to the head portion through a snap on connectioncomprising a slot in the tulip or saddle structure for receiving thehead portion.
 24. An implant for spinal fixation or fusion, the implantcomprising: a stem portion, a head portion, and a linear longitudinalaxis, the head portion including a shank with a length such that itextends through the stem portion and distally from the stem portion, theshank having a distal region with external threads that are shaped tointerface with corresponding internal threads on the stem portion, theimplant having a length and a configuration such that the stem extendsin a sacrum and across a sacroiliac joint when the implant is implantedwithin the sacrum, across the sacroiliac joint, and into an ilium. 25.The implant of claim 24, further comprising a tulip or saddle secured orsecurable to a proximal end region of the head portion, the implanthaving a length such that the tulip or saddle is disposed outside of thesacrum when a distal end of the shank is in the ilium.
 26. The implantof claim 25, further comprising a rod that is sized and shaped to besecured to the tulip or saddle when the distal end of the shank is inthe ilium.
 27. The implant of claim 24, wherein the implant includes aproximal region with external threads.
 28. The implant of claim 24,wherein the stem portion has a triangular cross sectional areatransverse to the linear longitudinal axis.